Field of the Invention
The present invention relates to a printed circuit board mounted with a bare chip.
Background Art
Printed circuit boards in which wiring is formed on a substrate using a printed conductor and which are mounted with electronic parts are used in the fields of various electronic devices and electric devices. Downsized printed circuit boards on which parts are densely mounted allow electronic devices and electric devices to be reduced in thickness and size. In recent years, there are proposals on structures in which a part such as a semiconductor device or sensor stripped of a package, that is, a bare chip part is mounted on a printed wiring board in order to further reduce the thickness and size of the devices. There are also proposals on techniques whereby a bare chip is mounted in a recessed part provided on a top surface of a printed wiring board (e.g., Japanese Patent Laid-Open No. 8-321567 (see pp. 9 and 10, FIG. 1 and FIGS. 3 to 6)).
Conventionally, the interior of a recessed part in which a bare chip part is mounted is filled and sealed with resin. For this reason, wiring on the surface of the bare chip part or a wire connecting the bare chip part and a printed conductor of a printed wiring board may be deformed or peeled off due to a pressure when the resin is applied or stress when the resin hardens, causing deterioration of reliability.
Moreover, a dielectric constant of the resin causes a capacitance of wiring or between wires of the bare chip part to increase, and therefore high-frequency performance of the bare chip part deteriorates. For example, when the capacitance between wires on the surface of the bare chip part increases, leakage of a high-frequency signal between wires increases, causing an increase of noise included in an output signal from the bare chip part.